Michael is 28 years older than Stephanie. Three years ago, Michael was 5 times as old as Stephanie. How old is Stephanie now?
Answer: We can use the given information to write down two equations that describe the ages of Michael and Stephanie. Let Michael's current age be $m$ and Stephanie's current age be $s$ The information in the first sentence can be expressed in the following equation: $m = s + 28$ Three years ago, Michael was $m - 3$ years old, and Stephanie was $s - 3$ years old. The information in the second sentence can be expressed in the following equation: $m - 3 = 5(s - 3)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $s$ , it might be easiest to use our first equation for $m$ and substitute it into our second equation. Our first equation is: $m = s + 28$ . Substituting this into our second equation, we get the equation: $(s + 28)$ $-$ $3 = 5(s - 3)$ which combines the information about $s$ from both of our original equations. Simplifying both sides of this equation, we get: $s + 25 = 5 s - 15$ Solving for $s$ , we get: $4 s = 40$ $s = 10$.